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Published: Mon, 5 Dec 2016

Electricity is an essential energy source for modern living. Disruption to supply or isolation can lead to the development of alternative methods of obtaining this essential energy resource. For electrical energy to be useful it must be harnessed through the use of an electrical circuit and an energy-converting appliance.

As electricity became increasingly used as the main power supply in homes and electrical appliances became an integral part of daily life for many Australians, the dangers associated with electricity became more prominent. Voltages as low as 20 volts can be dangerous to the human body depending on the health of the person and length of time of contact with the current. Safety devices in household appliances and within the electric circuits in the home can prevent electrical injury or assist in reducing the potential for electric shock.

This module increases students’ understanding of the history, nature and practice of physics and the applications and uses of physics.

Electrical Energy in the Home

1. Society has become increasingly dependent on electricity over the last 200 years

Discuss how the main sources of domestic energy have changed over time

The main sources of domestic energy have changed greatly through the years. As population grew each new energy sources gave more power, more wealth, better living conditions and more opportunity for humans.

Assess some of the impacts of changes in, and increased access to, sources of energy for a community

Before only man power was used, there was hardly any leisure time, but due to industrialization, there has been a lot of mass production which has greatly decreased human effort and giving us more leisure time.

Discuss some of the ways in which electricity can be provided in remote locations

Solar cells – A solar cell converts sunlight directly to electricity which can be stored in batteries for night use.

Wind Turbines – Generate electricity from the power of the wind.

Identify data sources, gather, process and analyse secondary information about the differing views of Volta and Galvani about animal and chemical electricity and discuss whether their different views contributed to increased understanding of electricity.

www.wikipedia.org

Luigi Galvani conducted a series of experiments with animals, beginning with dissected frogs.

Galvani carried out a wide ranging series of experiments which found that there were convulsive movements of the frog when two metals were made to touch each other while one metal was in contact with a nerve and the other was in contact with a muscle of the frog. Galvani came to the conclusion “that the electricity was inherent in the animal itself”.

According to Galvani, this conclusion was strengthened by “an observation that a kind of circuit of a delicate nerve fluid is made from the nerves to the muscles when the phenomenon of contractions is produced, similar to the electric circuit which is completed in a Leyden jar”(2). The diagram to the left illustrates Galvani’s theory (3). Galvani published the results of his experiments in a book called (Commentary on the Effect of Electricity on Muscular Motion).

When Alessandro Volta read Galvani’s “Commentary,” however, he came to a different conclusion. Volta focused on the two different kinds of metal used in the basic versions of Galvani’s experiments. The diagram to the left shows Volta’s theory that the electricity originated in the bimetal arc itself, here drawn in two distinctly different shades, and that the resulting flow of electricity produced the muscular contractions (3). Volta’s subsequent experiments led to the development of the voltaic cell–similar to a modern-day car battery–and to the development of the field of electrochemistry. Much of our current knowledge of chemical reactions can be traced almost directly to the experiments of Galvani and Volta.

Electrical Energy in the Home

2. One of the main advantages of electricity is that is can be moved with comparative ease from one place to another through electric circuits

Describe the behaviour of electrostatic charges and the properties of the fields associated with them

Electro static charges push or pull each other……. There are forces between them:

Same charges: Repel

Opposite Charges: Attract

Field between two charged plates

The forces are best explained by imagining that each electric charge is surrounded by a force field. Any electric charge that is placed within the field will experience a force.

By definition the direction of the force field lines is the direction a positive (+VE) charge would move if placed in the field.

Define the unit of electric charge as the coulomb

The unit of electric charge is the coulomb (C). 1 coulomb of charge is a very large amount, so “microcoulombs”(uC) are commonly used.

1(uC)=1 times 10 to the power of -6 C

Define the electric field as a field of force with a field strength equal to the force per unit charge at that point:

ð¸ = electric field strength (Newton/coulomb) (NC-1)

ð¹ = force (Newton) (N)

ð‘ž = electric charge (coulomb) (C)

Since force is measured in newtons (N), and charge is in coulombs (C), it follows that the unit of electric field strength is the “newton per coulomb” (NC to the power of -1).

This means if a charge “Q” experiences an electric force “F”, then there must be an electric field present, and its strength is F/Q.

Define electric current as the rate at which charge flows (coulombs/ second or amperes) under the influence of an electric field

Current is the rate at which charge flows. 1 ampere = 1 coulomb/second Conventional current runs from + to -. The electron movement is in the opposite direction of conventional current.

Identify that current can be either direct with the net flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forwards periodically

Direct Current:

If the electric field is constant, then the charge will flow steadily in one direction. This is called direct current (DC) e.g. Batteries.

Alternating Current:

If a fields keeps reversing its direction, so does the current. The charges will move back and forth. This is called alternating current (AC). Generators produce AC.

Describe electric potential difference (voltage) between two points as the change in potential energy per unit charge moving from one point to the other (joules/coulomb or volts)

Discuss how potential difference changes at different points around a DC circuit

Decreases as it move around the circuit.

Identify the difference between conductors and insulators

Conductor: A conductor is something with low resistance, thus current can flow through it easily. Generally metals are good conductors. Silver and Gold are excellent conductors, but we mostly use copper and aluminium for electrical wiring, this is because they are nearly as good as conductors and a lot cheaper.

Insulator: An insulator is mostly a total opposite of a conductor. It has very high resistance, thus which impedes current flow. Example of good insulators includes glass, plastic, and paper. Although their resistance is very high, it’s all a matter of Ohm’s Law. If a large enough voltage is applied, even a good insulator can “break down” and allow current to flow.

Define resistance as the ratio of voltage to current for a particular conductor:

The unit of resistance is called the “Ohm”. The symbol used is the greek letter “omiga”. How this relates to voltage and current is due to Ohm’s Law.

Describe qualitatively how each of the following affects the movement of electricity through a conductor:

– length

Everything else being equal, the longer conductor has more resistance, thus meaning less conductivity.

– cross sectional area

The larger the cross-sectional area, the less resistance, thus meaning greater conductivity.

– temperature

Generally in metals, the hotter they get, the more resistance they develop, thus meaning increasing conductivity.

– material

Metals are mostly good conductors while things such as glass and plastic are poor.

Present diagrammatic information to describe the electric field strength and direction:

– between charged parallel plates

– about and between a positive and negative point charge

Solve problems and analyse information using:

Plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the relationship between voltage across and current in a DC circuit

Solve problems and analyse information applying:

Plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the variations in potential difference between different points around a DC circuit

Gather and process secondary information to identify materials that are commonly used as conductors to provide household electricity

www.wikipedia.com

Copper: A ductile, malleable, reddish-brown metallic element that is an excellent conductor of heat and electricity and is widely used for electrical wiring, water piping, and corrosion-resistant parts, either pure or in alloys such as brass and bronze. Atomic number 29; atomic weight 63.54; melting point 1,083°C; boiling point 2,595°C; specific gravity 8.96; valence 1, 2.

Aluminium: (Symbol Al)

A silvery-white, ductile metallic element, the most abundant in the earth’s crust but found only in combination, chiefly in bauxite. Having good conductive and thermal properties, it is used to form many hard, light, corrosion-resistant alloys. Atomic number 13; atomic weight 26.98; melting point 660.2°C; boiling point 2,467°C; specific gravity 2.69; valence 3.

Electrical Energy in the Home

3. Series and parallel circuits serve different purposes in households

Identify the difference between series and parallel circuits

Series Circuit:

In a series circuit all the components are connected in series or connected one after the other, where the current can only take a single path. If 3 light bulbs are in a series circuit, the light bulbs are either all on, or all off. They cannot be switched independently. If one bulb “burn out” the circuit is broken and they all go out.

Parallel Circuits:

In a parallel circuit all components are arranged in separate branches of the circuit. Where the current can take multiple paths. If 3 bulbs are arranged in a parallel circuit, at each branch the current divides and flows through one bulb only and each bulb can be switched on/off separately, and if one “burns out”, the others continue to work.

Compare parallel and series circuits in terms of voltage across components and current through them

In series circuits the current is the same throughout the circuit i.e. IT = I1 = I2. Voltages are different across different resistors, but they add up to the for the circuit i.e. VT = V1 + V2.

In parallel circuits the voltages are all the same across each resistor i.e. VT = V1 = V2 = V3. Currents are different in each branch but add to the total current i.e. IT = I1 + I2 + I3.

Identify uses of ammeters and voltmeters

Ammeters:

An instrument for the measurement of electric current. The unit of current, the ampere, is the base unit on which rests the International System (SI) definitions of all the electrical units. The operating principle of an ammeter depends on the nature of the current to be measured and the accuracy required. Currents may be broadly classified as direct current (dc), low-frequency alternating current (ac), or radio frequency.

Voltmeters:

An instrument for the measurement of the electric potential difference between two conductors. Many different kinds of instruments are available to suit different purposes.

Explain why ammeters and voltmeters are connected differently in a circuit

Ammeters measure the current, thus they would have to be placed series with the component you wish to measure current flow through.

Voltmeters are placed differently in a circuit as it measures the potential difference across a component and therefore must be placed in parallel with it.

Explain why there are different circuits for lighting, heating and other appliances in a house

In a typical modern home is wired to contain a number of separate circuits. Each circuit may contain lights or power outlets and all of them are wired in parallel.

The reason why mostly everything is wired in parallel is because it has many advantages, such advantages are that they can be switched on and off independently. If one burns out the other keep going and the total resistance of the parallel circuit is less, and more usable power can be delivered to each light or appliance.

Plan, choose equipment or resources for and perform first-hand investigations to gather data and use available evidence to compare measurements of current and voltage in series and parallel circuits in computer simulations or hands-on equipment

Electrical Energy in the Home

4. The amount of power is related to the rate at which energy is transformed

Explain that power is the rate at which energy is transformed from one form to another

Mathematically power = energy divide by time so P = E/t or E = P.t

Identify the relationship between power, potential difference and current

P = VI

Power = Voltage x Current

P = E/t

Power = Energy/Time

Power is measured in Watts (W).

Identify that the total amount of energy used depends on the length of time the current is flowing and can be calculated using:

Energy = VIt

If you combine the equation P= VI and P=E/t then it follows that VI=E/t and therefore, E=V.I.t

Explain why the kilowatt-hour is used to measure electrical energy consumption rather than the joule

The reason why the kilowatt-hour which is a unit of energy which is the expenditure of one kilowatt of power for one hour. The reason why this is used instead of joules is because electrical is consumed widely and extensively meaning large amount of consumption, the appropriate measurement for such a large amount of consumption, kilowatt-hour is the most appropriate measurement unit.

Perform a first-hand investigation, gather information and use available evidence to demonstrate the relationship between current, voltage and power for a model 6V to 12V electric heating coil

Solve problems and analyse information using:

P=VI

and

Energy = VIt

Question: If electricity cots 15c per kWh calculate i) the energy consumed ii) the cost of using: a 100W globe and a 1kW radiator for 3 hours.

Solution:

i) (100 + 1000) Ã- 3 Ã- 60 Ã- 60= 11880000J OR 11.88MJ

ii) 1.1kW Ã- 3 Ã- 0.15 = $0.495

Electrical Energy in the Home

5. Electric currents also produce magnetic fields and these fields are used in different devices in the home

Describe the behaviour of the magnetic poles of bar magnets when they are brought close together

Define the direction of the magnetic field at a point as the direction of force on a very small north magnetic pole when placed at that point

Describe the magnetic field around pairs of magnetic poles

There is always a North-pole and there is always a South-pole. Magnetic fields are always shown visually as lines of force that give a definite pole at each end of the material where the flux lines are more dense and concentrated. The lines which go to make up a magnetic field showing the direction and intensity are called Lines of Force or more commonly “Magnetic Flux” and are given the Greek symbol, Phi ( Î¦ ) as shown below.

Describe the production of a magnetic field by an electric current in a straight current-carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines

When current is passed through a conductor, a magnetic field is created around it. The direction of the magnetic field can be found using the right hand rule. Point your right hand thumb in the direction of the current and the direction of your fingers is the direction of the magnetic field.

Compare the nature and generation of magnetic fields by solenoids and a bar magnet

In a solenoid the wire is wrapped into a helix or coil, the magnetic field in each loop adds to its neighbours to intensify the field. The magnetic field of a solenoid is exactly the same shape as a bar magnet.

Plan, choose equipment or resources for, and perform a first-hand investigation to build an electromagnet

Perform a first-hand investigation to observe magnetic fields by mapping lines of force:

– around a bar magnet

– surrounding a straight DC current-carrying conductor

– a solenoid

– present information using and to show the direction of a current and direction of a magnetic field

Electrical Energy in the Home

6. Safety devices are important in household circuits

Discuss the dangers of an electric shock from both a 240 volt AC mains supply and various DC voltages, from appliances, on the muscles of the body

An electric shock form a 240 volt AC mains supple can kill a person while various DC voltages form appliances for example 50V can disrupt nerve signals and send your muscles into spasms and if the muscle involved in your heart, it can go into “fibrillation” where it quivers uncontrollably and does not pump blood properly…….a potentially lethal situation.

Describe the functions of circuit breakers, fuses, earthing, double insulation and other safety devices in the home

A fuse is a short piece of wire which is used to break circuits as this has a low melting point and if an excess of current flows through it, it gets hot, which it then melts and thereby breaks the circuit.

Circuit breakers on the other hand do the same job as a fuse, but can be “re-set” after a circuit overload causes them to “trip”.

Earthing is where a power point and most plugs have 3 slots/pins the 3rd is for the “earth” wire. The earth wire carries no current and does nothing. But, if however a loose wire or faulty insulation allows an appliance to become “live” with electricity, then the current is conducted safely by the earth wire down into the ground.

Double insulation is when two layers of insulation which is used to shield electrical circuits form human contact, so if a fault occurred in small hand-held appliance, even with a earth wire a person can still get shocked.

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